Optical networks have become a standard technology for the transport of information in the telecommunications industry. A number of different optical network standards have been defined, with each having advantages and disadvantages for different uses. Synchronous optical network (SONET) is one standard for optical telecommunications transport. SONET is expected to provide the transport infrastructure for worldwide telecommunications for at least the next two or three decades. The increased configuration flexibility and bandwidth availability of SONET provides significant advantages over the older telecommunications system, such as reduction in equipment requirements, increase in network reliability, ability to carry signals in a variety of formats, a set of generic standards that enable products from different vendors to be connected, and a flexible architecture capable of accommodating future applications, with a variety of transmission rates. SONET is often used for long-haul, metro level, and access transport applications.
One common feature of a SONET network is the provision of two independent optical fiber communication paths between any two points. One fiber communication path is known as the Working path and the other fiber path is known as the Protection path. Signals are input to and output from the Working and Protection paths using multiplexing circuits, which provides the interfaces between the different network signals and SONET signals. The main advantage of this arrangement is its survivability; if a fiber path is cut, the multiplexers have the intelligence to send the services affected via an alternate path without interruption. For example, is signals are being sent over the Working path and the Working path is cut, the signals may be sent over the Protection path without loss of service.
A problem that arises with SONET networks having both a Working path and a Protection path is that the bandwidth of the path that is not being used is essentially wasted. For some applications of a SONET network, the protection from service interruption may be worth the expense and complexity of supporting the path having the wasted bandwidth. However, for many applications a need arises for a more cost and bandwidth efficient technique.